1. Field of the Invention
The present invention relates polystyrene blends. The present invention particularly relates to polystyrene blends prepared using a solution blend process.
2. Background of the Art
Polystyrene is one of the largest volume thermoplastic resins in commercial production today. Unmodified polystyrene is well suited to applications where its brittleness is acceptable. Engineering plastics have been used in applications where less brittleness is required, but such polymers are often expensive or have properties other than less brittleness that make them less than optimum selections. Thus, styrene-based copolymers, and particularly polystyrene resins that are modified with organic rubber particles, have been investigated for use in applications requiring less brittleness. The modification of polystyrene to reduce brittleness is often referred to increasing its impact properties and thus the modified polystyrene is said to have higher impact.
These high-impact polystyrene blends, commonly referred to by the acronym HIPS, are known to be useful in the art of preparing articles with polymers wherein the application for the articles requires less brittleness than unmodified polystyrene. For example, U.S. Defensive Publication T59,011 to Smith discloses that a high impact resin can be prepared by blending from 15 to 50 parts of an impact modifier with from 85 to 50 parts of a clear crystal polystyrene. Such materials are disclosed to be useful for packaging applications.
Another method of making HIPS is to first dissolve a rubber in styrene monomer and then polymerize the monomer. Such polymers are disclosed in U.S. Pat. No. 6,569,941 to Sosa, et al. Therein, it is disclosed that styrene monomer containing a dissolved polybutadiene rubber is flowed into an elongated upflow stirred reactor containing three reaction zones, wherein the styrene monomer is polymerized to form a HIPS.
It is also known to blend polystyrene with other materials. For example, U.S. Pat. No. 5,194,525, to Miura et al, discloses a continuous process for making polystyrene from styrene monomer and a polymerizable unsaturated fatty acid. The inclusion of the unsaturated fatty acid is disclosed to improve the heat resistance and moldability of the blend, making the modified polystyrene desirable for injection molding applications.
In HIPS, desirably the polystyrene is a continuous phase including a discontinuous phase of rubber particles. The size and distribution of the rubber particles in the continuous polystyrene phase can affect the properties of the HIPS. In blends of polystyrene with other materials, the distribution of the noncontinuous phase in the continuous polystyrene phase is often similarly important.